The present invention relates generally to cutting tools for boring holes, and more particularly to a drill point geometry such as on a spade blade drill, and its method of manufacture.
Spade blade drills are generally known in the art and use replaceable spade blade inserts to form the cutting edges of the drill point. Conventional inserts, or blades, may incorporate web-thinning notches on either side of a blade tip. The notches lead into flutes. Conventional inserts may use both primary and secondary relief surfaces to reduce or eliminate the chisel. Chip splitting grooves may be provided across the relief surfaces. Conventionally, the profile of the chip splitters is somewhat frusticonical with a generally circular valley. Slight variations in the dimensions or arrangement of the point geometry may have a significant affect on the drill life and performance.
The present invention provides a spade blade drill having an insert with a blended open notch form that intersects the back of the rake face and that is generally concave throughout the notch, back from the cutting edge, and a controlled notch lip length to notch hook length ratio, which leads to enhanced chip evacuation and a reduced heat flux due to an increased heat transfer surface area.
In one aspect of the present invention, the spade blade insert has a reduced clearance relief angle at its lands and elliptical profiled flutes and open round profiled chip splitters to reduce chip packing and curling.
These and other features and advantages of the invention will be more clearly understood from the following detailed description and drawings of preferred embodiments of the present invention.